1. Field of the Invention
The invention relates to a process for the production of functional coatings of organofunctional silanes and a coating material for producing coated substrates.
2. Description of the Prior Art
Thermally curable coating materials for plastic surfaces based on polysiloxane, which lead to improved mechanical characteristics such as scratch resistance and abrasion resistance, have already been used commercially for a considerable time (cf. J. Hennig xe2x80x9cKratzfest beschichtete Kunststoffexe2x80x9d in Kunststoffe 71, 1981, p.103). However, the use of the coating materials described therein is partly limited by the low thermal stability of organic polymeric materials, so that for thermally less stressable thermoplastics, such as e.g. ABS, PS PVC, PUR, PE, PP, etc., UV-curable coating materials have been developed (cf. K. Greiwe in xe2x80x9cBetter Ceramics through chemistry Vxe2x80x9d published by M. J. Hampden-Smith, W. G. Klemperer and C. J. Brinker, xe2x80x9cCharacterisation of hydrolysed Alkoxysilanes and Zirconiumalkoxides for the development of UV-curable scratch-resistant coatingsxe2x80x9d in Mat. Res. Soc. Symp. Proc. Vol. 271, 1992, p.725). These polysiloxane-based, UV-curable materials are completely suitable for the above-indicated plastics in certain use cases as a result of their faster curing and lower thermal stressing, but fail to completely cover the use range of polysiloxane-based functional protective coatings.
DE 4,025,215 describes an alkali-stable and abrasion-resistant polysiloxane-based coating. The material is obtained by reacting organic epoxides with aminofunctional alkoxy silanes. However, the coating material only has a limited pot life and must therefore be used relatively quickly following its manufacture. DE 3,828,098 A1 describes a lacquer and a process for the production of scratch-proof coatings. Although this process leads to coatings, which offer satisfactory results with respect to numerous characteristics (e.g. scratch resistance, transparency, good primary adhesion to substrates), improvements are necessary to such coatings for numerous applications.
The main disadvantages of these systems are the lack of permanent adhesion of the thus produced coatings to substrates, as well as an inadequate pot life of the lacquers.
In the case of different corrosive stresses (particularly in alkaline aqueous solutions), the adhesion of such coatings deteriorates down to the complete detachment of the coating and consequently the protection (e.g. abrasion and corrosion protection) for the particular substrate is no longer guaranteed. The lacquers according to DE 3,828,098 A1 have such a short pot life that, if the described good characteristics are to be obtained, must be processed within a few hours (max. 8 h) and must therefore be directly produced in situ.
The problem of the present invention, based on DE 3,828,098, is to provide a coating material and a process for the production of functional coatings on substrates, which compared with the known coating materials has a permanent adhesion even under unfavourable corrosive conditions, whereby simultaneously good stratch and abrasion resistances are required. In addition, the coating material must have an increased pot life, so that it can be processed over a longer period of time extending to several weeks.
With respect to the process, this problem is solved, for example, by a process for the production of abrasion resistant functional coatings utilizing organofunctional silanes, a metal compound and difficultly volatile oxides, comprising the steps of:
a) performing a hydrolytic condensation, optionally in the presence of a condensation catalyst and/or additives, of the following components
1) at least one crosslinkable, organofunctional silane of formula (II)
Rxe2x80x2xe2x80x3mSiX(4xe2x88x92m)xe2x80x83xe2x80x83(II)
in which the groups X, being the same or different, stand for hydrogen, halogen, alkoxy, acyloxy, alkylcarbonyl, alkoxycarbonyl or xe2x80x94NRxe2x80x32 (Rxe2x80x3=H and/or alkyl) and the radicals Rxe2x80x2xe2x80x3, being the same or different, stand for alkyl, alkenyl, alkynyl, aryl, arylalkyl, alkylaryl, arylalkenyl, alkenylaryl, arylalkynyl or alkynylaryl, in which the Rxe2x80x2xe2x80x3 radicals can be interrupted by O or S-atoms or the group xe2x80x94NRxe2x80x3, the Rxe2x80x2xe2x80x3 radicals can carry one or more substituents from the group of halogens and optionally substituted amino, amide, aldehyde, keto, alkylcarbonyl, carboxy, mercapto, cyano, hydroxy, alkoxy, alkoxycarbonyl, sulphonic group, phosphoric group, acryloxy, methacryloxy, epoxy or vinyl groups and m has the value 1,2 or 3 and/or an oligomer derived therefrom, in which the radical Rxe2x80x2xe2x80x3 and/or the substituent is a crosslinkable radical or substituent, in a quantity of 10 to 95 mole %, based on the total number of moles of the monomeric starting component;
2) at least one metal compound of general formula III
MeRyxe2x80x83xe2x80x83(III)
in which Me is a metal selected from Al, Zr, or Ti, in which y in the case of Al aluminium is 3 and zirconium and titanium is 4 and the radicals R, which can be the same or different, stand for halogen, alkyl, alkoxy, acyloxy or hydroxy, in which said groups can be wholly or partly replaced by chelating ligands or an oligomer derived therefrom or an optionally complexed metal salt of an inorganic or organic acid, in a quantity of 5 to 75 mole %, based on the total number of moles of the monomeric starting component;
3) optionally at least one non-crosslinkable organofunctional silane of formula I
Rxe2x80x2mSiX(4xe2x88x92m)xe2x80x83xe2x80x83(I)
in which the groups X, which can be the same or different, stand for hydrogen, halogen, hydroxy, alkoxy, acyloxy, alkylcarbonyl, alkoxycarbonyl or xe2x80x94NRxe2x80x32(Rxe2x80x3=H and/or alkyl) and the radicals Rxe2x80x2, which can be the same or different, stand for alkyl, aryl, arylalkyl or alkylaryl, in which said Rxe2x80x2 radicals can be interrupted by O or S-atoms or the group xe2x80x94NRxe2x80x3, the Rxe2x80x2 radicals also can carry one or more substituents from the group of halogens and optionally substituted amide, aldehyde, keto, alkylcarbonyl, carboxy, cyano, alkoxy or alkoxycarbonyl groups and m has the value 1,2 or 3 and/or an oligomer derived therefrom, in a quantity of 0 to 60 mole %, based on the total number of moles of the monomeric starting components; and
4) optionally one or more difficultly volatile oxides, soluble in the reaction medium, of an element of the main group Ia to Va or the auxiliary groups IIb, IIIb, Vb to VIIb of the periodic system, with the exception of Al, and/or one or more compounds of one of these elements soluble in the reaction medium and forming a difficultly volatile oxide under the reaction conditions, in a quantity of 0 to 70 mole %, based on the total number of moles of the monomeric starting component;
b) adding to said hydrolytic condensate an organic, crosslinkable prepolymer, said crosslinkable prepolymer being completely an unblocked prepolymer, the reacting, crosslinkable groups of radical Rxe2x80x2xe2x80x3 or the crosslinkable substituent at the radical Rxe2x80x2xe2x80x3 being crosslinkable with identical reaction groups at the prepolymer and the prepolymer is added in a quantity of 2 to 70 mole %, based on the total number of moles of the monomeric starting component, thereby resulting in a coating solution; and
c) applying and subsequently curing the coating solution on a substrate. Advantageous further developments are described herein.
It is essential to the invention that through the use of the crosslinkable, organic silane of general formula II (component 1) in conjunction with the crosslinkable prepolymer, an additional, organic crosslinking occurs. It has surprisingly been found that the latter crosslinking is responsible for obtaining an excellent permanent adhesion, even when there is simultaneously a corrosive action. At the same time a greatly extended pot life is obtained. According to the preferred embodiment of claim 2, it is particularly advantageous if the metal compound of general formula III (component 2) is used in chelated form. This further increases the pot life. As a result of this measure the coating material can be processed for several weeks.
According to a preferred embodiment, it is advantageous if the viscosity of the coating material is adjusted to a value of 5 to 50 mPaxc2x7s. Thus, it is decisive in the present substrate coating process, that the organofunctional silane of general formula II is crosslinked by an additional organic crosslinking with the aid of a purely organically crosslinkable prepolymer. Both the radical Rxe2x80x2xe2x80x3 and the corresponding substituent of the organofunctional silane of general formula II are responsible for said crosslinking. Therefore the crosslinking can start from the radical Rxe2x80x2xe2x80x3 or the substituent of the radical Rxe2x80x2xe2x80x3. However, preferably the crosslinking starts from the substituent.
The groups X in the general formulas I and II, which can be the same or different, can be hydrogen, halogen, alkoxy, acyloxy, alkylcarbonyl, alkoxycarbonyl or NRxe2x80x32, in which Rxe2x80x3 is hydrogen or alkyl.
The non-crosslinkable radicals Rxe2x80x2, which can be the same or different, are either alkyl, aryl, arylalkyl or alkylaryl. These radicals can be interrupted by O or S-atoms or the NRxe2x80x3 group and carry one or more non-crosslinkable substituents from the group of halogens and the optionally substituted amide, aldehyde, keto, alkylcarbonyl, carboxy, cyano, alkoxy or alkoxycarbonyl groups. Alkyl radicals are e.g. straight-chain, branched or cyclic radicals with 1 to 20 preferably I to 10 carbon atoms and in particular lower alkyl radicals with 1 to 6 and preferably 1 to 4 carbon atoms. Specific examples are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec.-butyl, tert.-butyl, isobutyl, n-pentyl, n-hexyl, dodecyl, octadecyl and cyclohexyl.
Preferably, in the silanes of general formula I, the index m=1. In the case of higher values of m, there is a risk of a reduction in the hardness of the material, if too much such silane is used.
Specific examples for the organofunctional silanes of formula I are: bis-(dimethylamino)-methyl, phenyl silanes, bis-(mono-n-butylamino)-dimethyl silanes, 2-chloroethyl trichloro silanes, 2-chloroethyl methyl dichloro silanes, di-n-butyl dichloro silanes, diethyl diethoxy silanes, ethyl trimethoxy silanes, 8-bromooctyl trichloro silanes, 3-bromopropyl trichloro silanes, t-butyl-trichloro silanes, 1-chloroethyl trichloro silanes, chloromethyl trichloro silanes, chlorophenyl trichloro silanes, cyclohexyl trichloro silanes, dimethyl dichloro silanes, diphenyl dichloro silanes, ethyl dichloro silanes. Particular preference is given to phenyl trimethoxy silane, aminopropyl triethoxy silane and propyl trimethoxy silane. All the silanes are commercially obtainable, e.g. from ABCR GmbH and Co., Postfach 210135, D-7500, Karlsruhe 21.
In the organofunctional silanes of general formula II (component 1), X and m have the meanings given hereinbefore. The radical Rxe2x80x2xe2x80x3 or the substituent must be such that it is suitable for crosslinking. The radical Rxe2x80x2xe2x80x3 can be: alkyl, alkenyl, alkinyl, aryl, arylalkyl, alkylaryl, arylalkenyl, alkenylaryl, arylalkinyl or alkinylaryl. These radicals can be interrupted, as in the case of the organofunctional silane of general formula I, by 0 or S-atoms or the NRxe2x80x3 group. The radical Rxe2x80x2xe2x80x3 can also carry one or more crosslinkable substituents from the group of halogens and the optionally substituted amino, amide, aldehyde, keto, alkylcarbonyl, carboxy, mercapto, cyano, hydroxy, alkoxy, alkoxycarbonyl, sulphonic acid, phosphoric acid, acryloxy, methacryloxy, epoxy or vinyl groups.
Specific examples for a crosslinkable, organofunctional silane of general formula II are vinyl trimethoxy silane, aminopropyl triethoxysilane, isocyanatopropyl triethoxy silane, mercaptopropyl trimethoxy silane, vinyltriethoxy silanes, vinyl ethyl dichloro silanes, vinyl methyl diacetoxy silanes, viny methyl dichloro silanes, vinyl methyl diethoxy silanes, vinyl triacetoxy silanes, vinyl trichloro silanes, phenyl vinyl diethoxy silanes, phenyl allyl dichloro silanes, 3-isocyanotopropyl triethoxy silanes, methacryloxy propenyl trimethoxy silanes and 3-methacryloxy propyl trimethoxy silanes. Particular preference is given to methacryloxy propyl trimethoxy silane and 3-glycidyloxy propyl trimethoxy silane. These and further silanes can be obtained from the same manufacturer as indicated hereinbefore.
Metal compounds usable according to the invention are in particular those with the empirical formula MeRy (III), in which the radicals R, which can be the same or different, stand for halogen, alkyl, alkoxy, acryloxy or hydroxy. Examples of preferred metals are Al, Ti or Zr and y is then either 3 for Al or 4. Particular preference is given to Al. Preferably (claim 2) the metal compounds of general formula (III), before undergoing hydrolytic condensation, are chelated with a standard chelating ligand in the ratio 1:0.5-2. A ratio of approximately 1:1 has proved advantageous. The chelating ligand can be any standard chelating ligand, particularly acetyl acetone or ethyl acetoacetate.
Specific examples for metal compounds usable according to the invention are e.g. disclosed in DE 3,828,098 or 3,407,087, which are then chelated with the corresponding chelating ligands.
In place of the monomeric starting silanes, it is optionally possible to also use precondensed oligomers of said silanes, which are soluble in the reaction medium, i.e. straight-chain or cyclic, low molecular weight partial condensates (polyorganosiloxanes) with a degree of condensation of e.g. approximately 2 to 100, particularly approximately 2 to 6. The same applies with respect to the metal component (III). It is also possible to use fluorinated silanes, as described in EP 358,011 A2.
As the fourth component, the reaction medium can optionally contain soluble, difficultly volatile oxides or, compounds forming such difficultly volatile oxides of elements of the main group Ia to Va or their auxiliary groups IIb, IIIb, Vb to VIIIb of the periodic system of elements, with the exception of aluminium. Among the difficultly volatile oxides particular preference is given to B2O3, P2O5 and SnO2.
For crosslinking purposes use is made of prepolymers, in which the reacting, crosslinkable groups of the radical Rxe2x80x2xe2x80x3 and/or the crosslinkable substituents at the radical Rxe2x80x2xe2x80x3 can be crosslinked with the reacting groups at the prepolymer and these preferably include xe2x80x9clikexe2x80x9d prepolymers.
According to the invention the term like, crosslinkable prepolymers are understood to mean those in which the reacting groups are identical. In the case of epoxy group-containing silanes, use is made of epoxy resin, whilst in the case of acrylic group-containing silanes use is made of acrylates and generally acrylates are used in the case of acryloxy group-containing radicals. In the case of vinyl radicals or radicals with other polymerizable double bonds, prepolymers with crosslinkable double bonds are used.
The invention also covers the following crosslinking possibilities:
mercapto group-containing silanes and prepolymers with crosslinkable double bonds,
isocyanate group-containing silanes and polyols,
hydroxy group-containing silanes and isocyanates,
amino group-containing silanes and epoxy resins.
In part, mixtures of epoxy group-containing silanes and epoxy resins also contain silanes with aminoalkyl radicals. Here the amino group can crosslink both with the epoxy unit at the silane and with the epoxy resin.
For producing the coating the organofunctional silanes of general formula II and optionally I are stirred under ice cooling. Following this the metal compound of general formula III is chelated or a chelating ligand is added and then hydrolytic condensation takes place. To the reaction mixture is then added a prepolymer crosslinkable with the radical Rxe2x80x2xe2x80x3. Preferably the viscosity of the mixture is set to the desired value using conventional lacquer solvents. The thus obtained mixture is then applied to a substrate and cured.
For the production of the coating according to the invention, it is preferable to use 10 to 95, particularly 20 to 90 and with particular preference 30 to 90 mole % of component 1, 5 to 75, particularly 5 to 60 and in particularly preferred manner 10 to 40 mole % of component 2 and 0 to 60, particularly 0 to 50 and in particularly preferred manner 0 to 40 mole % of component 3 and max. 0 to 70 and preferably max. 0 to 40 mole % of component 4.
Component 1, in accordance with claim 1, is the crosslinkable silane of general formula II, component 2 the metal compound of formula III and component 3 the non-crosslinkable silane of general formula I.
It is particularly advantageous (claim 3), if hydrolytic condensation is performed in such a way that there is a hydrolytic precondensation with a lower water quantity than the quantity stoichiometrically required for complete hydrolysis of the hydrolyzable groups and then the prepolymer is added and subsequently further condensation takes place by adding further water, which partly or wholly brings about the hydrolysis of the remaining hydrolyzable groups.
Preferably precondensation takes place in the presence of a condensation catalyst. With respect to the performance of the process by means of precondensation, reference is made to DE-OS 3,828,098. The present invention also includes all condensation catalysts of the aforementioned document.
The processing of the coating material can now take place either immediately or only after a few weeks. As a result of the preferred inventive use of the chelated metal compound, it is possible to keep the coating material processable over a period of several weeks. Coating can then take place using all prior art processes, such as dipping, flow coating, pouring, centrifuging, spraying, rolling or brushing on. The. substrates for the coating can be random materials such as e.g. metals, plastics, ceramics, glass, paper or wood. The coating can be applied in different layers of e.g. I to 100 or preferably 2 to 30 xcexcm. It is preferable (claim 10) for the hardened coating to be subsequently treated chemically and/or physically, preferably with laser (UV) radiation.
The invention also relates to the substrates coated by the process according to the invention. According to the invention, for this purpose substrates are coated using the above-described process.
The invention also relates to a coating material for producing coatings on substrates. According to the characterizing features of claim 12 from the above-described organofunctional silanes a hydrolytic condensate is produced and then in a second stage to said hydrolytic condensate is added an organic, crosslinkable prepolymer of the corresponding radical Rxe2x80x2xe2x80x3. As in the process, it is again preferable for the hydrolytic condensation to be performed firstly as a hydrolytic precondensation of components 1 to 4 with a smaller water quantity than that necessary for complete hydrolysis, followed by the addition of the prepolymer and further condensation.
The coating material can contain conventional additives (claim 15) and condensation catalysts. With regards to the conventional additives it is preferable to use organic thinners, flow-control agents, colouring agents, UV-stabilizers, fillers, viscosity regulators, lubricants, spreading agents, sedimentation inhibitors, oxidation inhibitors or mixtures of these substances. Preferably in the case of the preferred embodiment according to claim 3, precondensation takes place in the presence of dcondensation catalyst. The condensation catalyst can be in the form of amines and compounds splitting off hydroxyl ions or protons. The invention also incorporates the condensation catalysts disclosed in DE-OS 3,828,098. According to claim 17 it is advantageous to set the viscosity at 0 to 50 and in particular to approximately 15 mPaxc2x7s.
With the coating material according to the invention or with the inventive process for producing coated substrates, coatings on substrates are obtained which, besides high scratch and abrasion resistance and excellent adhesion to different substrates (particularly glass and different metals) are in particular characterized by permanent adhesion (following various weather resistance tests) and good stability with respect to alkaline solutions. The characteristics of the coated material are maintained, even if it is only applied after a certain storage time (several weeks). As the viscosity of the coating material only rises very slowly (from approximately 12 to approximately 17 mPaxc2x7s after storing for 6 weeks), even after 6 weeks storage, it is possible to obtain coatings having excellent characteristics.
In addition, the coating material can be very adequately coloured using known dyes and can be processed to screen printable pastes by adding aerosils and optionally paint pigments (as a function of requirements).
Dyes soluble in alcoholic-aqueous solutions are particularly preferred. Such dyes are e.g. commercially available from Ciba-Geigy under the name Orasol dyes.
Preferably the coating material is also suitable for the application of a barrier layer with respect to H2S.
A preferred embodiment of the present invention discloses a process for the production of abrasion resistant functional coatings utilizing organofunctional silanes, a metal compound and difficultly volatile oxides. The process includes the following steps:
a) performing a hydrolytic condensation, optionally in the presence of a condensation catalyst and/or additives, of the following components
1) at least one crosslinkable, organofunctional silane of formula (II)
Rxe2x80x2xe2x80x3mSiX(4xe2x88x92m)xe2x80x83xe2x80x83(II)
in which the groups X, being the same or different, stand for hydrogen, halogen, alkoxy, acyloxy, alkylcarbonyl, alkoxycarbonyl or xe2x80x94NRxe2x80x32(Rxe2x80x3=H and/or alkyl) and the radicals Rxe2x80x2xe2x80x3, being the same or different, stand for alkyl, alkenyl, alkynyl, aryl, arylalkyl, alkylaryl, arylalkenyl, alkenylaryl, arylalkynyl or alkynylaryl, in which the Rxe2x80x2xe2x80x3 radicals can be interrupted by O or S-atoms or the group xe2x80x94NRxe2x80x3, the Rxe2x80x2xe2x80x3 radicals can carry one or more substituents from the group of halogens and optionally substituted amino, amide, aldehyde, keto, alkylcarbonyl, carboxy, mercapto, cyano, hydroxy, alkoxy, alkoxycarbonyl, sulphonic group, phosphoric group, acryloxy, methacryloxy, epoxy or vinyl groups and m has the value 1,2 or 3 and/or an oligomer derived therefrom, in which the radical Rxe2x80x2xe2x80x3 and/or the substituent is a crosslinkable radical or substituent, in a quantity of 10 to 95 mole %, based on the total number of moles of the monomeric starting component;
2) at least one metal compound of general formula III
MeRyxe2x80x83xe2x80x83(III)
in which Me is a metal selected from Al, Zr, or Ti, in which y in the case of Al aluminium is 3 and zirconium and titanium is 4 and the radicals R, being the same or different, stand for halogen, alkyl, alkoxy, acyloxy or hydroxy, in which said groups can be wholly or partly replaced by chelating ligands or an oligomer derived therefrom or an optionally complexed metal salt of an inorganic or organic acid, in a quantity of 5 to 75 mole %, based on the total number of moles of the monomeric starting component;
3) optionally at least one non-crosslinkable organofunctional silane of formula I
Rxe2x80x2mSiX(4xe2x88x92m)xe2x80x83xe2x80x83(I)
in which the groups X, which can be the same or different, stand for hydrogen, halogen, hydroxy, alkoxy, acyloxy, alkylcarbonyl, alkoxycarbonyl or xe2x80x94NRxe2x80x32(Rxe2x80x3=H and/or alkyl) and the radicals Rxe2x80x2, being the same or different, stand for alkyl, aryl, arylalkyl or alkylaryl, in which said Rxe2x80x2 radicals can be interrupted by O or S-atoms or the group xe2x80x94NRxe2x80x3, the Rxe2x80x2 radicals also can carry one or more substituents from the group of halogens and optionally substituted amide, aldehyde, keto, alkylcarbonyl, carboxy, cyano, alkoxy or alkoxycarbonyl groups and m has the value 1,2 or 3 and/or an oligomer derived therefrom, in a quantity of 0 to 60 mole %, based on the total number of moles of the monomeric starting components; and
4) optionally one or more difficultly volatile oxides, soluble in the reaction medium, of an element of the main group Ia to Va or the auxiliary groups IIb, IIIb, Vb to VIIIb of the periodic system, with the exception of Al, and/or one or more compounds of one of these elements soluble in the reaction medium and forming a difficultly volatile oxide under the reaction conditions, in a quantity of 0 to 70 mole %, based on the total number of moles of the monomeric starting component;
b) adding to said hydrolytic condensate an organic, crosslinkable prepolymer, said crosslinkable prepolymer being completely an unblocked prepolymer, the reacting, crosslinkable groups of radical Rxe2x80x2xe2x80x3 or the crosslinkable substituent at the radical Rxe2x80x2xe2x80x3 being crosslinkable with identical reaction groups at the prepolymer and the prepolymer is added in a quantity of 2 to 70 mole %, based on the total number of moles of the monomeric starting component, thereby resulting in a coating solution; and
c) applying and subsequently curing the coating solution on a substrate.
The process described above is a preferred process for carrying out the invention. It is preferred that the organic crosslinkable prepolymer be completely unblocked. It is also preferred that the reacting crosslinkable groups of radical Rxe2x80x2xe2x80x3 and/or the crosslinkable substituent at the radical Rxe2x80x2xe2x80x3 are identical to and crosslinkable with those at the prepolymer. Also preferred are coatings made from the process as described above, or equivalent processes.
The following examples serve to illustrate the invention.